1. Field of the Invention
The present invention relates to a method for reclaiming a lost wax composition which is used in a lost wax precision casting process. In particular, this invention relates to a method for recovering a filler containing only an extremely small amount of ash, from a filler-containing waste lost wax composition generated during a dewaxing process using an autoclave.
2. Description of Related Art
Lost wax precision casting is a known method of carrying out precision casting in industry. According to this method, at first, either a silicon rubber matrix or a die is used to prepare a pattern using wax, so as to obtain a wax pattern having the same shape as the final product. Then, the wax pattern is coated with a refractory ceramic material, followed by a dewaxing process in which the wax pattern is heated so as to elute the wax, thereby obtaining a casting mold. Molten metal is then poured into the casting mold so as to produce various precision products.
For dewaxing in such methods, there has long been widely used a steam dewaxing method since this method is effective for recovery and reclamation of the wax. According to this method, the casting mold coated with a ceramic material is introduced into an autoclave, and is heated in steam to a temperature of 150 to 180xc2x0 C. In this manner, the wax may be melted so as to be discharged.
The wax discharged from the dewaxing process is thus recovered and is then subjected to a reclaiming treatment so as to obtain reclaimed wax which can again be used in preparing a wax pattern. To improve heat conductivity and to prevent shrinkage at thick portions of a wax pattern, it has been suggested to include in the lost wax composition an organic filler formed of a polystyrene and having an average diameter of 40 xcexcm, with its content being twenty to thirty percent of the lost wax composition. However, as the organic filler is expensive, it has become more and more desired to recover and reclaim not only the wax component but also the filler component.
However, no viable techniques have been proposed to recover the wax component together with the filler component from the waste wax composition. On the other hand, an improved method has been suggested and put into practical use, as suggested by the inventors of the resent invention in Japanese Unexamined Patent Application Publication No. 11-192534 (U.S. Pat. No. 6,066,250). According to that method, an amount of waste wax composition containing the filler and/or an amount of residue formed by separating or extracting the wax component from the wax composition are required to be dissolved and dispersed in an organic solvent, so that a solution is thus formed. After that, the solution is separated into a phase (fraction) in which the wax has been dissolved (a dissolved wax fraction) and another phase (fraction) containing solid and wax components. Subsequently, the wax component and the organic solvent are removed from the phase containing solid and wax components, thereby obtaining desired reclaimed filler. The reclaimed filler is then treated in an aqueous alkaline solution, thus obtaining an amount of refined filler having a high purity.
With the use of the above method, it has become possible to recover the filler from the waste lost wax composition, so that it is possible to reuse the recovered filler. However, the waste wax composition usually contains some solid components such as sand and iron, and also contains various other additives used in a lost wax casting process, such as a colloidal silica for use as an adhesive agent and CaO for use as a disintegrator. For this reason, there has been a demand that the above solid components and various other additives be removed as completely as possible in order to ensure a high purity for the filler.
In fact, the method taught by U.S. Pat. No. 6,066,250 has proven to be relatively capable of meeting the above requirements. However, as will be appreciated from the results of further research conducted by the inventors of the present invention and described below, the recovered filler still contains some solid components which fail to be completely removed therefrom. As a result, it has become clear that if the recovered and refined filler is used by itself, it would be difficult to solve the above problems sufficiently.
Accordingly, it is an object of the present invention to provide a method of treating the waste wax composition and/or remaining materials (wax recovery residue) formed by separating or extracting the wax component from the filler-containing waste wax composition, so as to recover and reclaim the filler, while almost completely removing the impurities coming from the lost wax casting mold, thereby recovering a filler of a lost wax composition at an extremely high purity.
Specifically, the inventors of the present invention have found that iron and calcium are contained in an impurity component of recovered filler, and it is possible to dissolve and thus remove the impurity by dispersing the recovered filler into an acidic aqueous solution. The present inventors have further discovered that if a surface active agent such as a detergent is added at a time when a crude reclaimed filler is dispersed into an aqueous alkaline solution, the dispersion of the wax component into the aqueous alkaline solution is promoted, so that the refining of the filler component can be made much easier. Moreover, the present inventors have also found that an appropriate adjustment of the concentration of the aqueous alkaline solution will allow an easier separation for separating the solid impurities from the filler component.
The present invention is therefore a method of recovering and refining a filler of a lost wax composition, comprising: separating a crude reclaimed filler, in which one or both of i) a waste wax composition containing a filler, and ii) a residue formed by separating or extracting a wax component from the waste wax composition, are dissolved and/or dispersed in an organic solvent, the whole system is then separated into a dissolved wax phase and a solids/wax-containing fraction, thereby removing and thus recovering the wax component and the organic solvent component from the solids/wax-containing fraction; said method further comprising: a) an alkali-washing process wherein the crude reclaimed filler is dispersed in an aqueous alkaline solution, so as to dissolve and thus remove some impurities soluble in an alkaline solution; b) an acid-washing process wherein the crude reclaimed filler is dispersed in an acidic aqueous solution so as to dissolve and thus remove some impurities soluble in an acid. Further, it is preferred that subsequent to the alkali-washing process and the acid-washing process, a water-washing process is carried out for washing the filler component with water.
At this time, it is preferred that during the alkali-washing process, a surface active agent is added in to the aqueous alkaline solution, thereby enhancing the dispersion of the crude reclaimed filler in the alkaline solution.
Further, during the alkali-washing process, the specific gravity of the alkaline solution is adjusted to be larger than that of the wax component, but smaller than the specific gravity of the filler component. In this way, the separation and the removal of the wax component attached to the crude reclaimed filler will become much easier, thereby making it possible to more efficiently separate and remove the solid impurities.
Further, according to the present invention, there is provided another method of recovering and refining a filler of a lost wax composition, said method comprising: separating a crude reclaimed filler, in which one or both of i) a waste wax composition containing a filler, and ii) a residue formed by separating or extracting a wax component from the waste wax composition, are dissolved and thus dispersed in an organic solvent, the whole system being then separated into a dissolved wax phase and a solids/wax-containing fraction, thereby removing and thus recovering the wax component and the organic solvent component from the solids/wax-containing fraction; alkali-washing wherein the crude reclaimed filler obtained in the above process is dispersed in an aqueous alkaline solution, a surface active agent being added to the alkaline solution, so as to dissolve and thus remove some impurities soluble in an alkaline solution; a water-washing process wherein the filler treated in the alkali-washing process is washed with water so as to obtain a refined filler. Therefore, it is possible to more completely separate and remove the solid impurities in the alkali-washing process.
In addition, according to the present invention, the solids/wax-containing fraction may be a phase containing an aqueous phase. In this way, the water removal treatment, which is otherwise needed for treating and thus removing the water contained in the waste wax composition, can be dispensed with.